The present invention relates to a fault diagnosis apparatus for a UPC circuit, and more particularly to a fault diagnosis method of a UPC circuit controlling a flow rate of a stream flow of cells on the basis of prescribed information relative to cell traffic.
A so-called ATM (asynchronous transfer mode) technology is now being developed for performing asynchronous transfer of a cell, which is a kind of fixed length packet. In the ATM network, a subscriber makes a declaration about his cell traffic to a central terminal, and the central terminal effects control of a flow rate of the stream flow of cells on the basis of the declaration. This control is called usage parameter control or UPC and is an indispensable technology for successfully operating the ATM network.
FIGS.1 and 2 show various methods of the usage parameter control mentioned above. FIG.1(A) shows a time interval method, in which time intervals t.sub.1, t.sub.2 between arrivals of cells are measured and a determination is made as to whether or not a traffic excess exists by comparing the measurement results with a prescribed time T. FIG.1(B) shows a T-X method, in which numbers x.sub.1, x.sub.2 of cells arriving during a prescribed period T are counted, and a determination is made as to whether or not a traffic excess exists by comparing the counts with a prescribed cell count X. FIG.1(C) shows a DB (dangerous bridge) method, in which numbers x.sub.1 -x.sub.6 of cells arriving during each of prescribed time intervals T and having their phases shifted by .DELTA.t with respect to each other are counted, .DELTA.t being a time period required for one cell to pass, and a determination is made as to whether or not traffic excess exists by comparing the counts with a prescribed cell count X.
FIG.2(A) shows a CAT-M method. In the case illustrated in FIG.2(A), time intervals t.sub.1 -t.sub.5, having their phases shifted with respect to each other upon each arrival of a cell are measured until the number of arriving cells is equal to the number obtained by adding 1 to a prescribed cell count X, and a determination is made as to whether or not a traffic excess exists by comparing the measurement results with a prescribed time T. FIG.2(B) shows a LB method. In the case illustrated in FIG.2(B), a count is incremented by one upon each arrival of a cell while, at the same time, the count is continuously decremented by a prescribed rate, and a determination is made as to whether or not a traffic excess exists by comparing the count value of a counter and a prescribed count B.
FIG.3 illustrates the configuration of a conventional usage parameter control method and, more specifically, shows an example where the DB method of FIG.1(C) is employed. The DB method, allows control to be applied to an ATM cell, which control resembles the control of the number of people who can walk across a "dangerous bridge" at the same time. In this method, the number of cells that can coexist at a given moment on a bridge is designated as X, the parallel of which bridge is realized by a cell time having a duration of T.
The UPC circuit shown in FIG.3 comprises a cell information branching part 1 (SB) for causing the input cell information to branch; a cell delay part 2 (SM) for delaying the input cell; a cell control part 3 (SC) for effecting control by which a cell passes through control part 3 unmodified, or is abandoned, or has a marking applied thereto; a bridge memory 4 (BM) for recording information relative to a cell; operating S-UPC circuits 20.sub.w1 -20.sub.wm 1 each being equipped with one traffic measuring part; an OR gate circuit (13) for giving a determination that an input cell be abandoned on the basis of the comparison result, outputted by a comparator 56 provided in each of the operating S-UPC circuits 20.sub.w1 -20.sub.wm, and for feeding the determination result to the input of the cell control part 3.
A parameter memory (PM) 50 of the S-UPC circuit 20.sub.w1 stores: a VPI parameter (virtual path identifier) of an object cell, a declared time interval (an order value of a time interval) T and a declared cell count (an order value of cell count) X. When a cell on a highway arrives at a point of time, the cell information branching part 1 causes a predetermined header information (for example, VPI: virtual path identifier) to branch the cell off to the cell delay part 2 and to the S-UPC circuits 20.sub.w1 -20.sub.wm. The cell delay part 2 delays the cell by a time period necessary for determination of the existence of the traffic excess as described above. An object cell filter (SF) 52 makes a discrimination as to whether or not the VPI information that has branched agrees with the VPI parameter of its own, and, if there is an agreement, outputs a discrimination pulse V. Upon the output of the discrimination pulse V, the count of a counter (CTR) 55 is incremented. The bridge memory 4 stores a chronological record of the past VPI information going back a maximum cell time length of T.sub.MAX. On the basis of the order value T, a selector (SEL) 54 reads out, from the bridge memory 4, the VPI information going back the cell time length of T. An object cell filter (SF) 53 makes a discrimination as to whether or not the read VPI information agrees with the VPI parameter of its own, and, if there is an agreement, outputs a discrimination pulse V'. Upon receiving the output of the discrimination pulse V', the count of the counter 55 is decremented.
Thus, the counter 55 continuously counts the number x of cells arriving during prescribed time periods T having their phases shifted by the one-cell pass time .DELTA.t with respect to each other. A signal x indicating the cell count and output by the counter 55 is fed, when prompted by the discrimination pulse V, to the input of the comparator (CMP) 56. The comparator 56, upon comparing the cell count x with the order value X, outputs a control signal D.sub.w1 to the cell delay part 2 in case x&gt;X holds, thereby causing the cell inputted to the cell delay part 2 to have a marking applied thereto or be abandoned. If x&gt;X does not hold, the comparator 56 does not output the control signal D.sub.w1. Accordingly, the cell inputted to the cell delay part 2 is allowed to pass unmodified through the control part 3. The same description holds true of the other S-UPC circuits 20.sub.w2 -20.sub.wm.
As has described above, the conventional art allows a total of m UPC circuits to effect a total of m kinds of usage parameter. It results from this that the conventional art has a disadvantage in that it is not capable of detecting a failure in the traffic measuring part of, for example, the counter circuit, thereby causing the UPC circuits to proceed with false usage parameter control.
The same problem arises not only in the DB method but also in the time interval method, the T-X method, the CAT-M method, and the LB method.
Moreover, the UPC circuit employing the conventional DB method and effecting control using a single bridge memory has a disadvantage in that it is not capable of detecting a failure in the bridge memory, thereby possibly causing the UPC circuits to proceed with false usage parameter control.